First boil the potatoes in a pan or steamer or pressure cooker. then peel and mash them when still warm.

Heat oil in a frying pan. add the mustard..
allow the mustard seed to splutter
add the chopped onion and saute till they are translucent and soften.
now add the ginger-garlic paste, curry leaves and green chilies. saute for a minute.
add the turmeric powder, asafoetida and stir. now add the coriander leaves and stir.

Add the potatoes to this mixture or add this sauted mixture to the potatoes. stir well.
if there is moisture, then you can cook the potato mixture for a few minutes.
add lemon juice & salt. mix well.

Check the seasoning and add more salt or red chili powder or lemon juice if required.

Make medium sized balls from this mixture.
prepare a thick flowing batter with all the ingredients mentioned above in the 'for the batter' list.

Heat oil for deep frying in a kadai or pan. dip each potato ball in the batter and coat it well with the batter.

Add the batter coated potato balls in the medium hot oil.
fry till golden on both sides. drain on paper towels to remove excess oil.
serve hot with tamarind chutney or tomato ketchup.